Clamping apparatus for molding machine

ABSTRACT

An apparatus for pressure molding or casting comprising a plurality of strain rods and having an adjustable fixed back plate mounted at one end of said rods, a fixed platen at the other end, and a movable platen slidably mounted over the rods intermediate the fixed plate and fixed platen, the movable platen and fixed plate being adapted to support the halves of a mold. A pair of cylinder and piston combinations are coaxially mounted on the adjustable fixed back plate, one arranged to provide rapid reciprocal motion of the movable platen, and the other arranged to provide a large clamping force or tonnage. Means is provided for transmitting the clamping force or tonnage to the movable platen comprising a plurality of compression or stress rods affixed at one end to the movable platen, and a rotatable lock plate mounted on the adjustable fixed back plate adapted in one rotative position to engage the free ends of the compression rods and in another to permit the stress rods to pass therethrough.

United States Patent [191 Dangremond et al.

[ Oct. 30, 1973 CLAMPING APPARATUS FOR MOLDING MACHINE [73] Assignee:Ex-Cell-O Corporation, Detroit,

Mich.

[22] Filed: Nov. 11, 1971 [21] Appl. No.: 197,694

[52] US. Cl. 425/450, 425/DIG. 221, 425/DIG. 223 [58] Field of SearchB29f/l/00; 425/450, 425/242, 168, DIG. 221, DIG. 223, 167

Primary Examiner-J. Spencer Overholser Assistant Examiner-David S.Safran Att0rneyRoy A. Plant et al.

[57] ABSTRACT An apparatus for pressure molding or casting comprising aplurality of strain rods and having an adjustable f eddaack platemounted at one end of said rods, a fixed platen at the other end, and amovable platen slidably mounted over the rods intermediate the fixedplate and fixed platen, the movable platen and fixed plate being adaptedto support the halves of a mold. A pair of cylinder and pistoncombinations are coaxially mounted on the adjustable fixed back plate,one arranged to provide rapid reciprocal motion of the movable platen,and the other. arranged to provide a large clamping force or tonnage.Means is provided for transmitting the clamping force or tonnage to themovable platen comprising a plurality of compression or stress rodsaffixed at one end to the movable platen, and a rotatable lock platemounted on the adjustable fixed back plate adapted in one rotativeposition to engage the free ends of the compression rods and in anotherto permit the stress rods to pass therethrough.

6 Claims, 10 Drawing Figures PATENTED BN3 0 I973 SHEET 2 or 4 CLAMPINGAPPARATUS FOR MOLDING MACHINE BACKGROUND OF THE INVENTION The inventionrelates to an apparatus or machine for use in molding or casting, as forexample for use in injection molding utilizing molds or dies comprisedof separable members, and more specifically refers to a machine or thetype described having improved means for applying tonnage force forcompressing the mold members, and improved means for transmitting thetonnage force to the movable platen of the apparatus.

Machines of the present type designed for clamping the members of a moldfor molding or casting are generally of two types, depending upon themeans utilized for developing and applying the clamping force ortonnage. One type is the mechanical type utilizing mechanical means fordeveloping extremely large forces required for clamping. The most commonform of the mechanical type utilizes a toggle mechanism which developslarge forces through an arrangement of levers. The toggle-type clamp isfast-acting, provides instantaneous lockup at the end of the strokewhich brings the mold parts together, and provides rapid separation ofthe molds after the molding process is complete. The toggle-type alsohas lower initial cost and in some cases lower operating cost. Foroperations of smaller molding machines, that is utilizing clampingforces of up to 300 tons, the toggle-type has been most popular.However, in the case of larger machines where clamping forces or tonnageof from 450 to 2700 tons are required, the toggle-type of machine hasnot been found to be satisfactory because of the need for longer stroke.For machines requiring such higher clamping forces and longer stroke,the hydraulic type of machine is generally utilized. Such machinescomprise generally a small cylinder for providing large movement of themovable platen for closing the mold, and a second cylinder of largerdiameter for providing the large clamping force or tonnage. The varioushydraulic types of molding machines disclosed in the art have beensuccessful in providing the desired clamping tonnage, but have severaldisadvantages. First, they are relatively slow acting. Second, theygenerally require a large volume of oil for operating the tonnagecylinder. This is particularly objectionable when deep draw dies areutilized requiring a long stroke clamping apparatus.

SUMMARY OF THE INVENTION Accordingly, it is an object of the presentinvention to provide a hydraulically operated apparatus for clampingmolds and dies utilized for molding or casting plastic materials ormetals, capable of providing large clamping tonnage.

It is another object to provide an apparatus of the type described whichutilizes only a small amount of hydraulic fluid for operating thetonnage cylinder.

It is still another object of the invention to provide improved meansfor operating the movable platen of an apparatus having a long stroke sothat the apparatus may be utilized with deep draw molds.

It is still an additional object to provide an apparatus providinghigh-speed reciprocal travel of the movable platen.

It is still another object to provide an apparatus of the type describedhaving an improved quick-acting structure for transmitting tonnage forceto the movable platen, and for providing rapid release of the clampingtonnage and withdrawal of the movable platen after the molding operationis complete.

It is still another object of the invention to provide an apparatus ofthe type described capable of offering reliable high precision operationwith relatively little maintenance over extended periods of time.

It is still another object to provide an apparatus of the type describedwhich is less expensive to build and operate than comparable equipmentpresently utilized in the art.

Still further objects and advantages of the invention will appear as thedescription proceeds.

To the accomplishment of the foregoing and related ends, the invention,then, consists of the useful apparatus herein fully described andparticularly pointed out in the claims, the annexed drawings, and thefollowing description setting forth in detail a certain illustrativeembodiment of the invention, such disclosed embodiment illustrating,however, but one of the various ways in which the principle of theinvention may be used.

BRIEF DESCRIPTION OF THE DRAWINGS In the annexed drawings:

FIG. 1 is a side elevational view of the apparatus of the inventionadditionally showing an injection molding apparatus used in conjunctiontherewith, the platens being positioned for maximum die size.

FIG. 2 is a side elevational view showing the apparatus of the presentinvention, but excluding the injection molding apparatus, the platensbeing shown arranged for minimum die size.

FIG. 3 is a left end view of the apparatus shown in FIGS. 1 and 2.

FIG. 4 is a sectional view showing the apparatus in retracted positionand taken at the line 44 of FIG. 3, looking in the direction of thearrows.

FIG. 5 is a fragmentary sectional view similar to that of FIG. 4, butshowing the fast travel cylinder expanded.

FIG. 6 is a fragmentary sectional view similar to that of FIG. 5, buthaving the lock plate indexed.

FIG. 7 is a fragmentary cross-sectional view similar to that of FIG. 5,but showing the tonnage cylinder expanded.

FIG. 8 is a sectional view taken at the line 8-8 of FIG. 7, looking inthe direction of the arrows, showing a pressure pad adjacent to a stressrod clearance hole.

FIG. 9 is a sectional view taken at the line 99 of FIG. 4, looking inthe direction of the arrows, and showing the annular shape of thetonnage cylinder; and

FIG. 10 is a sectional view taken at the line 10l0 of FIG. 6, looking inthe direction of the arrows, and showing the lock plate indexingcylinder.

DESCRIPTION OF THE SPECIFIC EMBODIMENT Referring more particularly toFIGS. 1 and 2, the apparatus of the present invention 10 comprises abase 1 l and a base platform 12 having mounted thereon fixed ways 13 and14. A back plate 15 having a moving base 16 is provided with a track 17engaging a way 13. A movable platen 18 is mounted on a traveling base 19and provided with an engaging track 20 engaging ways 14. A stationaryplaten 21 is mounted on the base platform 12. A plurality of strain ortie rods 22, 23, 24 and 25 are each affixed at one end to the stationaryplaten 21. The other ends of the strain rods are slidably positioned inchannels provided in the back plate A molding material feed tube 26 ofthe injection molding machine is provided with a nozzle 27 which extendsinto a complementary receptacle provided in the stationary platen 21.The molding machine shown generally additionally has a hopper 28 and anextruder 29.

Mounted on the back plate 15 is a fast-acting cylinder 30 having aterminal cap 31, and a piston rod 32 engaging the movable platen 18. Thethreaded ends of the strain rods 22, 23, 24 and 25 which extend throughthe back plate 15 are engaged by a rotary adjustment unit 33. Stress orcompression rods 34, 35, 36 and 37 are each affixed at one end to themovable platen 18 and have their other ends extending in the directionof the back plate 15. A tonnage piston and cylinder assembly 38 ismounted on the forward portion of the back plate 15 having a lock plateand tonnage assembly 40 mounted immediately in front of the tonnagepiston and cylinder assembly 38.

Referring to FIG. 3, the device for adjusting the position of the backplate 15 is illustrated and comprises a plurality of nuts 42, 43, 44 and45 having peripheral gear teeth provided thereon, and an annular gear 46having peripheral teeth meshed with the teeth of the nuts 42-45.Adjustment of the position of the back plate 15 is accomplished byrotating the annular gear 46 through drive gear 101.

Referring specifically to FIG. 4, the fast-acting cylinder 30 is shownin greater detail and comprises, in addition to the cylinder 30, cap 31and piston rod 32, an elbow 47 having a passage 48 for passage ofhydraulic fluid. Additionally, a piston is contained within the cylinder30 affixed to the piston rod 32. A plurality of bolts 50 mount thecylinder to the back plate 15. Additionally shown in FIG. 4 are wearcaps affixed to the ends of the stress rods 34-37. The stress rods areslidably journaled in sleeves 57, 58, 59 and 60 (FIG. 9) to preventwear, to facilitate sliding when the movable platen is moved and toprovide sealing of the hydraulic fluid.

Referring to FIGS. 4, 5, 6, and 7, a supporting hub 61 is affixed to theback plate 15 by means of bolts 62. A bore is provided receiving thereduced end 63 of the cylinder wall 30. An elbow 64 is mounted on thesupporting hub 61 having a passageway 65 for passage of hydraulic fluidto provide for return of the fast travel cylinder. A packing gland 66provides a seal for the fast travel cylinder.

Referring to FIGS. 4-9, the annular shaped tonnage cylinder and pistonare shown. The inner cylinder wall 67 is a sleeve mounted over thesupporting hub 61 (FIG. 9). The outer cylinder wall 68 comprises theinner surface of a cylinder 78 mounted on the fixed plate 15 by means ofscrews 100. The front wall of the back plate 15 serves as the rear wallof the tonnage cylinder. The tonnage piston 69 (FIGS. 4-9) is slidablymounted in the tonnage cylinder 78. It engages the outer cylinder wall68, the inner cylinder wall 67 and the outer surfaces of the sleeves57-60. A tonnage piston cap 70 is mounted on the forward surface of thetonnage piston 69 by means of bolts 71. A hanger plate 72 is mounted onthe fixed plate 15 by means of bolts 73, the spacers 74. The hangerplate supports the ends of the stress rods 34, 35, 36 and 37 in theclamping position. Sleeves 75 are mounted in apertures provided in thehanger plate providing supporting seals for the stress rods. An outerretainer ring 79 is mounted on the tonnage cylinder 78 by means of thebolts 73 and spacers 74, providing a limit position for the tonnagepiston 69 by engaging a shoulder 76 thereof. An inner retainer 80engages and restrains the inner cylinder wall 67 of the tonnagecylinder.

Rotatably mounted over the inner cylinder wall 67 is a lock plate 81having clearance holes 82, 83, 84 and 85 for receiving the ends of thestress rods 34-37. Adjacent to the clearance holes are pressure pads 86,87, 88 and 89 affixed to the lock plate 81 by means of bolts 97. Abracket 90 is affixed to a flattened portion of the lock plate 81 bymeans of bolts 91. A hydraulic cylinder 92 is provided with a piston rod93 which is pivotally affixed to the bracket 90 by means of a clevis 94and pin 99. A flexible anchor 95 pivotally connects the cylinder 92 tothe back plate structure. The cylinder, piston and rod arrangement forrotating the lock plate must be mounted on a flexible joint, as forexample a ball joint, since during operation the lock plate movesaxially forwardly and rearwardly by a small amount. The structure mayadditionally be rubber mounted to provide the small necessary movement.

ADJUSTMENT OF THE APPARATUS FOR OPERATION To set up the apparatus of theinvention for normal operation, the fast travel cylinder 30 may beactuated for completely withdrawing the movable platen 18. The moldhalves are then mounted on the movable platen 18 and the fixed plate 21.The fast-acting cylinder 30 is then actuated to move the movable platentoward the stationary platen until the piston 49 of the fast-actingcylinder 30 is fully extended. The cylinder 92 is actuated to rotate thelock plate 81 to the position in which the pressure pads 86-89 aredisposed immediately behind the wear caps 55 of the stress rods 34-37.The annular gear 46 is then rotated, moving the back plate 15 forwardlyuntil the two halves of the mold are substantially in contact engagementor is desired, have only a small clearance between them. The lock plate81 is then rotated by actuation of the cylinder 92 tothe unlockedposition in which the clearance holes 82-85 are in register immediatelybehind the stress rods 34-37. The fast-acting cylinder 30 is thenactuated and the movable platen 18 is retracted to its rearwardmostposition. The nozzle 27 of the injection molding machine is theninserted into the receptacle provided in the stationary platen 21, andthe machine is ready for operation.

OPERATION OF THE APPARATUS Operation of the apparatus is normallycontrolled by automatic sequencing and timing devices which may beelectrically, electronically, or even fluidically operated. Since suchtiming and sequencing devices are well known in the art, they will notbe described herein.

Operation begins with the fast travel piston 49 in the position shown inFIG. 4, and with the movable platen 18 in its rearwardmost position. Theoperation cycle, which is controlled by automatic timing devices knownin the art as referred to above, begins with the actuation of thefast-acting cylinder 30 causing the piston 49 to move forwardly to itsfurthermost position, through a stroke of about 40 inches. The apparatusat this point is in the position shown in FIG. 5 with the piston 49forwardly disposed and the wear caps 55 of the stress rods 34-37 removedfrom the sleeves 57-60 and positioned in advance of the lock plate 81.The cylinder 92 is then actuated causing the lock plate 81 to rotate andto assume the position shown in FIG. 6 wherein the pressure pads 86-89are positioned immediately behind the wear caps 55 of, the stress rods34-37. At this point there is a small clearance between the pressurepads and the wear caps 55. Hydraulic fluid under pressure is thenapplied to the tonnage cylinder 78 through a tonnage oil inlet 96 shownin FIG. 8. This causes the tonnage piston 69 to move forward to theposition shown in FIGS. 7 and 8. In order to utilize as little hydraulicfluid as possible in moving the tonnage piston, the stroke of the pistonmay be designed to be inch or less, and even shorter strokes such asinch or less are feasible.,The apparatus described herein andillustrated in the drawings has been successfully operated at a tonnageforce of about 650 tons. However, apparatus'of the type described may beproperly designed to provide clamping tonnage having values far less orin excess of 650 tons, by decreasing or increasing the area of thetonnage cylinder and piston.

When full tonnage force has been attained, molten material from theinjection end of the machine is injected under high pressure through thefixed platen 21 and into the mold maintained between the movable platenl8 and fixed platen 21. After the mold has been filled, tonnage ismaintained until the material has sufficiently solidified. Then cylinder69 is decompressed by removing oil through inlet 96 and then thecylinder 92 is free to rotate the lock plate 81 and to place the ends ofthe stress rods 34-37 in registry with the clearance holes 82-85 of thesleeves 57-60. The fast-acting cylinder 30 is then actuated and themovable platen 18 retracted and returned to its rest position, therebyopening the mold members and permitting the molded piece to be removed.The apparatus is now ready to start another cycle with the fast-actingcylinder 30 being actuated to extend the movable platen until the moldmembers mate again. The lock plate 81 is then rotated to bring thepressure pads 86-89 once more in registry with the ends of the stressrods 34-37 and the entire cycle repeated.

It will be seen that the tonnage cylinder 78 is single acting, that is,no provision is made for the introduction of hydraulic fluid in front ofthe piston to return it to its rearward position. Consequently, afterthe lock plate is rotated and opened, the tonnage piston 69 remains inplace. As a result, in a succeeding cycle when the movable platen 18 isreturned to the position in which the mold members meet, because theengaging surfaces of the pressure pads 86-89 and the stress rods 34-37are convexly shaped, as the lock plate rotates engagement between thepressure pads and stress rods may cause the stress rods to move forwarda small amount and to cause the mold members to kiss. This can beavoided by a modification of the procedure described above in carryingout the molding cycle. ln the modified procedure, after the piece hassolidified, instead of immediately rotating the lock plate 81 to releasethe movable platen 18, the fast-acting cylinder 30 is actuated while thelock plate 81 is still in locked position. This causes the stress rodsto apply force against the pressure pads 86-89. The lock plate in turnbears against the tonnage piston cap 70 and tonnage piston 69, forcingthe tonnage piston to return to its retracted position. The lock plate81 is then rotated and the movable platen 18 returned to its retractedposition. When in the following cycle, the movable platen is returned toits forward position and the lock plate rotated to locked position, aclearance between the pressure pads 86-89 and wear caps 55 of the stressrods 34-37 remains, as shown in FIG. 6, thereby avoiding prematureengagement of the stress rods with the pressure pads and with the resultthat kissing of the mold members is prevented.

The present apparatus designed to be operated in conjunction withmolding machines for clamping mold members has many advantages overprior art machines designed for the same purpose. First of all, it hasthe advantage of most hydraulically operated machines, that extremelylarge tonnage forces can be generated. Further, it has a number ofadvantages over hydraulically operated machines used in the art in thatit provides a small quick-acting cylinder to provide a long stroke to beused for the molding of deep draw parts. However, it avoids the commondeficiencies of prior art hydraulic machines in that the presentinvention utilizes a tonnage cylinder having an extremely short stroke,as low as inch or less. Consequently, it takes only a relatively smallamount of hydraulic fluid to stroke the piston. Moreover, the piston maybe stroked in a very short period of time. This arrangement avoids thebulky and slow-acting tonnage cylinders of the prior art in which theentire stroke of the tonnage cylinder may be as great as 40 inches ormore, thereby requiring the pumping of a large amount of hydraulicfluid. The present invention has an additional advantage in that itprovides a novel rotatably mounted lock plate cooperating with aplurality of stress rods affixed to the movable platen for rapidly andpositively locking the apparatus and providing a positive transmissionof the tonnage force from the tonnage cylinder to the movable platen. Afurther advantage of the present apparatus is that it is relativelycompact since it does not require large bulky hydraulic fluid storagetanks, and does not require bulky locking devices. The apparatus may beconstructed from readily available materials and is not undulyexpensive.

While but one form of the invention has been shown and described, otherforms within the spirit and scope. of the invention will nowbe'apparen't to those skilled in the art. Therefore, the embodimentshown in the drawings is to be considered as merely setting forth theinvention for illustrativepruposes, and is not intended to limit thescope of the invention herein described and shown.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1. An apparatus for use in molding or casting and adapted to support andclamp together the mold members of a mold comprising:

1. a frame,

2. a pair of platens adapted to support said mold members including,

a. a fixed platen affixed at one end of said frame,

and

b. a movable platen slidably mounted on a medial portion of said frame,

3. a back plate adjustably affixed to said frame at the other endthereof,

4. means for providing rapid reciprocal movement of said movable platenbetween an advanced position of mold closure and a retracted position ofmold 7 opening comprising a fast-acting cylinder having a piston mountedtherein for reciprocal movement of relatively small bore and ofrelatively long stroke mounted on said back plate and having a pistonrod the remote end of which is affixed to said movable platen,

5. means for providing a high tonnage clamping force comprising atonnage cylinder mounted on said back plate coaxially positioned withrespect to said fast-acting cylinder and having a piston reciprocablymounted therein, said cylinder having a bore of large cross-sectionalarea and a stroke of relatively short travel; and

6. means for transmitting tonnage clamping force from said tonnagecylinder to said movable platen comprising a plurality of stress rodseach affixed at one end to said movable platen and extending in parallelrelationship in the direction of said back plate, said back plate andsaid tonnage cylinder and piston being provided with apertures havingseals therein permitting said stress rods to pass therethrough, and alock plate rotatably mounted on said back plate and means for rotatingsaid lock plate alternatively to one of two indexing positions, saidlock plate having a plurality of apertures so arranged that when saidlock plate is in the open index position the ends of said stress rodsmay pass therethrough, and when said lock plate is rotated to the closedindex position, the ends of said stress rods engage said lock plate andforce transmitted from said tonnage piston to said lock plate is in turntransmitted to said stress rods.

2. An apparatus according to claim 1 wherein metal disc form pressurepads are mounted on said lock plate and adapted to engage the ends ofsaid stress rods when said lock plate is in the closed index position.

3. An apparatus according to claim 2, wherein the ends of said stressrods are provided with wear caps.

4. An apparatus according to claim 1, wherein a hanger plate is mountedon said back plate having apertures provided therein for supporting saidstress rods.

5. In an apparatus for use in molding or casting and adapted to supportand clamp together the mold members of a mold, comprising an elongateframe, a fixed platen mounted at one end of said frame, a movable platenslidably mounted in a medial portion of said frame, a back plateadjustably affixed to said frame at the other end thereof, and a tonnagecylinder mounted on said back plate having a piston reciprocably mountedtherein, the improvement therein comprising means for transmittingtonnage clamping force from said tonnage piston to said movable platencomprising a plurality of stress rods each affixed at one end to saidmovable platen and extending in parallel relationship in the directionof said back plate, said back plate and said tonnage cylinder and pistonbeing provided with apertures having seals therein permitting saidstress rods to pass therethrough, and a lock plate rotatably mounted onsaid back plate and adapted to be engaged by said tonnage piston, havinga plurality of apertures so arranged that when said lock plate is in theopen index position the ends of said stress rods may pass therethrough,and when said lock plate is rotated to the closed index position theends of said stress rods engage said lock plate and force transmittedfrom said tonnage piston through said lock plate is in turn transmittedto said stress rods and said movable platen.

6. An apparatus according to claim 5, wherein said rotatable lock plateis provided with a hydraulic cylinder for rotating said plate.

1. An apparatus for use in molding or casting and adapted to support andclamp together the mold members of a mold comprising:
 1. a frame,
 2. apair of platens adapted to support said mold members including, a. afixed platen affixed at one end of said frame, and b. a movable platenslidably mounted on a medial portion of said frame,
 3. a back plateadjustably affixed to said frame at the other end thereof,
 4. means forproviding rapid reciprocal movement of said movable platen between anadvanced position of mold closure and a retracted position of moldopening comprising a fast-acting cylinder having a piston mountedtherein for reciprocal movement of relatively small bore and ofrelatively long stroke mounted on said back plate and having a pistonrod the remote end of which is affixed to said movable platen,
 5. meansfor providing a high tonnage clamping force comprising a tonnagecylinder mounted on said back plate coaxially positioned with respect tosaid fast-acting cylinder and having a piston reciprocably mountedtherein, said cylinder having a bore of large cross-sectional area and astroke of relatively short travel; and
 6. means for transmitting tonnageclamping force from said tonnage cylinder to said movable platencomprising a plurality of stress rods each affixed at one end to saidmovable platen and extending in parallel relationship in the directionof said back plate, said back plate and said tonnage cylinder and pistonbeing provided with apertures having seals therein permitting saidstress rods to pass therethrough, and a lock plate rotatably mounted onsaid back plate and means for rotating said lock plate alternatively toone of two indexing positions, said lock plate having a plurality ofapertures so arranged that when said lock plate is in the open indexposition the ends of said stress rods may pass therethrough, and whensaid lock plate is rotated to the closed index position, the ends ofsaid stress rods engage said lock plate and force transmitted from saidtonnage piston to said lock plate is in turn transmitted to said stressrods.
 2. a pair of platens adapted to support said mold membersincluding, a. a fixed platen affixed at one end of said frame, and b. amovable platen slidably mounted on a medial portion of said frame,
 2. Anapparatus according to claim 1 wherein metal disc form pressure pads aremounted on said lock plate and adapted to engage the ends of said stressrods when said lock plate is in the closed index position.
 3. Anapparatus according to claim 2, wherein the ends of said stress rods areprovided with wear caps.
 3. a back plate adjustably affixed to saidframe at the other end thereof,
 4. An apparatus According to claim 1,wherein a hanger plate is mounted on said back plate having aperturesprovided therein for supporting said stress rods.
 4. means for providingrapid reciprocal movement of said movable platen between an advancedposition of mold closure and a retracted position of mold openingcomprising a fast-acting cylinder having a piston mounted therein forreciprocal movement of relatively small bore and of relatively longstroke mounted on said back plate and having a piston rod the remote endof which is affixed to said movable platen,
 5. means for providing ahigh tonnage clamping force comprising a tonnage cylinder mounted onsaid back plate coaxially positioned with respect to said fast-actingcylinder and having a piston reciprocably mounted therein, said cylinderhaving a bore of large cross-sectional area and a stroke of relativelyshort travel; and
 5. In an apparatus for use in molding or casting andadapted to support and clamp together the mold members of a mold,comprising an elongate frame, a fixed platen mounted at one end of saidframe, a movable platen slidably mounted in a medial portion of saidframe, a back plate adjustably affixed to said frame at the other endthereof, and a tonnage cylinder mounted on said back plate having apiston reciprocably mounted therein, the improvement therein comprisingmeans for transmitting tonnage clamping force from said tonnage pistonto said movable platen comprising a plurality of stress rods eachaffixed at one end to said movable platen and extending in parallelrelationship in the direction of said back plate, said back plate andsaid tonnage cylinder and piston being provided with apertures havingseals therein permitting said stress rods to pass therethrough, and alock plate rotatably mounted on said back plate and adapted to beengaged by said tonnage piston, having a plurality of apertures soarranged that when said lock plate is in the open index position theends of said stress rods may pass therethrough, and when said lock plateis rotated to the closed index position the ends of said stress rodsengage said lock plate and force transmitted from said tonnage pistonthrough said lock plate is in turn transmitted to said stress rods andsaid movable platen.
 6. An apparatus according to claim 5, wherein saidrotatable lock plate is provided with a hydraulic cylinder for rotatingsaid plate.
 6. means for transmitting tonnage clamping force from saidtonnage cylinder to said movable platen comprising a plurality of stressrods each affixed at one end to said movable platen and extending inparallel relationship in the direction of said back plate, said backplate and said tonnage cylinder and piston being provided with apertureshaving seals therein permitting said stress rods to pass therethrough,and a lock plate rotatably mounted on said back plate and means forrotating said lock plate alternatively to one of two indexing positions,said lock plate having a plurality of apertures so arranged that whensaid lock plate is in the open index position the ends of said stressrods may pass therethrough, and when said lock plate is rotated to theclosed index position, the ends of said stress rods engage said lockplate and force transmitted from said tonnage piston to said lock plateis in turn transmitted to said stress rods.